System and method for supplying and dispensing bubble-free photolithography chemical solutions

ABSTRACT

A photolithography system includes a variable-volume buffer tank, a dispensing system connected to the buffer tank, and a valve configured to release gas from a head space of the buffer tank while blocking the release of liquid from the head space. A storage container has an opening at the bottom and drains to the buffer tank through that opening. The buffer tank has a storage capacity sufficient to receive the full contents of the storage container. The system supplies chemical solutions to the dispensing system while keeping the chemical solutions from contact with air and other gases.

BACKGROUND

The present disclosure relates to photolithography systems and systemsand methods for supplying chemicals to photolithography systems.

An essential tool for manufacturing integrated circuits with highcomponent device densities is photolithography. Photolithographyinvolves forming thin coatings. One of these coatings is a photoresist.Another commonly used coating is a bottom anti-reflective coating(BARC). These coatings are formed from liquid chemical solutions. Thechemical solutions are held in reservoirs from which the chemicalsolutions are dispensed as needed.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a photolithography system in accordance with some embodimentsof the present disclosure

FIG. 2-5 are variable-volume buffer tanks in accordance with variousembodiments.

FIG. 6 is a flow chart of a method of supplying a chemical solution to aphotolithography system in accordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the disclosure.Specific examples of components and arrangements are described below tosimplify the present disclosure. These are, of course, merely examplesand are not intended to be limiting. For example, the formation of afirst feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

It has been observed that bubbles and contaminants in photolithographychemical solutions can lead to device defects. Air in the head spaceover a photolithography chemical solution reservoir has been found to bea source of contamination. Nitrogen filling the head space over aphotolithography chemical reservoir has been found to be a cause ofbubbles. The present disclosure provides systems and methods forsupplying photolithography chemical solutions with little or no exposureto air and limited exposure to and contact with a pure nitrogenatmosphere that can cause bubbles.

The equilibrium concentration of nitrogen in a liquid solution isapproximately proportional to the partial pressure of nitrogen incontact with that solution. If a liquid solution is stored under purenitrogen at one atmosphere pressure for a sufficient period of time, itwill absorb nitrogen until the nitrogen concentration in solution is inequilibrium with nitrogen gas at one atmosphere. If the liquid solutionis then released into ambient air at one atmosphere, nitrogen willdesorb until its concentration has decreased approximately 22%. Air isonly 78% nitrogen. The desorbing nitrogen can form bubbles, particularlyif it was absorbed to equilibrium with nitrogen gas at a pressure aboveone atmosphere or at a temperature above ambient. In some systemsprovided by the present disclosure, photolithography chemical solutionsare exposed to a pure nitrogen atmosphere, but the exposure time andcontact area are limited to prevent nitrogen absorbing into the solutionto a concentration near equilibrium.

According to some embodiments of the present disclosure, avariable-volume buffer tank provides a reservoir for a photolithographychemical solution dispensing system. The buffer tank provides areservoir from which a chemical solution can be dispensed as neededwithout requiring a head space filled with gas. In some of theseembodiments, the buffer tank includes a venting system to release anygas that make its way into the buffer tank or emerges from the liquid inthe buffer tank as bubbles. In some of these embodiments, the buffertank is maintained at a positive pressure to facilitate the completeremoval of any gas.

According to some embodiments of the present disclosure, avariable-volume buffer tank receives the full contents of a chemicalsolution storage container with each refill operation, which preventsthe chemical solution from being contaminated by air or saturated withnitrogen while in a partially full storage container. The buffer tank issized accordingly.

FIG. 1 illustrates a photolithography system 100 according to someembodiments of the present disclosure. Photolithography system 100includes a photolithography chemical solution dispensing system 160 anda photolithography chemical supply system 101. Supply system 101 isitself an example according to some embodiments of the presentdisclosure. Supply system 101 includes a variable-volume buffer tank 145and chemical solution storage containers 105. Buffer tank 145 provides areservoir of a chemical solution 150 and makes chemical solution 150available on demand to dispensing system 160 through a fixed conduit147. Storage containers 105 replenish buffer tank 145 through a conduit119.

Dispensing system 160 dispenses chemical solution 150 onto the surfacesof wafers 180. Chemical solution 150 is a photolithography chemicalsolution. A photolithography chemical solution is a liquid chemicalsolution suitable for spin coating onto wafers 180 within aphotolithography process. In most embodiments, photolithography system100 includes a spin coater (not shown). Chemical solution 150 can be,for example, a photoresist solution, a bottom anti-reflective coating(BARC) solution, or a primer solution such as a solution of primer thatpromotes adhesion between a wafer surface and a photoresist.

In some embodiments, dispensing system 160 includes a pump 163. In someembodiments, dispensing system 160 includes other components commonlyincluded in a photoresist dispensing system. These other components caninclude, for example, a filter 165, a valve 167, and a suck-back valve169. Suck-back valve 169 is a valve functional to remove chemicalsolution 150 from dispensing tip 171 between dispensing operations.Dispensing system 160 draws chemical solution 150 from buffer tank 145through conduit 147.

Buffer tank 145 includes a container space 140 having one or moremovable boundaries, whereby the volume of the container space 140 canincrease as fluid is added and decrease as fluid is removed. FIG. 1provides an example in accordance with embodiments where a collapsibleliner 131 provides movable boundaries for container space 140. Containerspace 140 of FIG. 1 includes a rigid upper container space 144 and ahead space 143. Collapsible liner 131 is a bag-like container. In someembodiments, collapsible liner 131 is gusseted. Collapsible liner 131can be formed of any suitable material. A suitable material can be, forexample, polytetrafluoroethylene (PTFE). Variable-volume buffer tank 145further includes a rigid shell 129. Rigid shell 129 supports liner 131.Shell 129 can be formed of a rigid material, such as stainless steel orhigh density polyethylene (HDPE).

FIGS. 2-5 provide additional examples of designs for variable-volumebuffer tank 145. FIGS. 2 and 3 illustrate variable-volume buffer tanks145A and 145B in accordance with some embodiments in which avariable-volume container space 140 is formed in part by a piston 132within a cylinder 134. FIGS. 4 and 5 illustrate variable-volume buffertanks 145C and 145D in accordance with some embodiments in which avariable-volume container space 140 is formed in part by a flexiblematerial having accordion pleats 136. An advantage of these designs incomparison to ones featuring a collapsible liner 131 is that they havefewer folds in which bubbles can be trapped.

In some embodiments, a variable-volume buffer tank 145 is equipped witha venting system 128 for releasing gases from head space 143, wherebythe contents of container space 140 within buffer tank 145 are at alltimes entirely or nearly entirely liquid. Venting system 128 includes avalve 141 that substantially prevents the contents of buffer tank 145from coming into communication with ambient air. In some embodimentsupper surfaces 142 of container space 140 are sloped toward head space143 proximate venting valve 141 to facilitate the migration of anybubbles within container space 140 to head space 143 where they can bevented. Venting valve 141 release gas into a vent pipe 139 or directlyinto the atmosphere.

In some embodiments, venting valve 141 is a degassing valve. A degassingvalve is a valve designed to allow the passage of gas while blocking thepassage of liquid. In some embodiments, a degassing valve includes afloat and the valve closes when a liquid raises the float. In someembodiments, a degassing valve 141 is of a type that is functional toselectively vent gases even when pressures in head space 143 are greaterthan pressures in vent pipe 139.

In some embodiments, venting valve 141 is an electronically controlledvalve. An electronically controlled valve is operated by a controller137 as illustrated in FIG. 1. Controller 137 can take input from abubble detector 135. Bubble detector 135 detects bubbles in head space143. In some embodiments, bubble detector 135 uses ultrasound to detectthe presence of bubbles in head space 143. When bubbles are detected,controller 137 opens venting valve 141. When bubbles are no longerdetected or after a short period, controller 137 closes venting valve141. Mechanical degassing valves are simpler than electronicallycontroller valves, but an electronically controlled valve can providethe most thorough venting.

In some embodiments, buffer tank 145 maintains chemical solution 150within container space 140 at a positive pressure. A positive pressureis a pressure in excess of atmospheric and can facilitate venting ofbubbles. In some embodiments, a positive pressure is maintained bycontrolling an amount of a fluid 129 in the space between rigid shell121 and liner 131. In some embodiments, a positive pressure ismaintained by applying a mechanical force against the outside ofcontainer space 140. A mechanical force can be applied, for example,through the piston 132 shown in FIGS. 2 and 3 or by the platform 138shown in FIGS. 4 and 5. Examples of mechanical forces includes forcessupplied by springs, hydraulics, or counter weights.

In some embodiments, a positive pressure in container space 140 ismaintained passively. A passive system can operate through gravity. Inthe example of FIG. 3, the weight of piston 132 can maintain a positivepressure in container space 140. The tendency of gravity to flattenvariable-volume buffer tank 145C or 145D of FIGS. 4 and 5 can maintain apositive pressure in the container space 140 of those examples.

In some embodiments, buffer tank 145 includes a pressure-regulatingsystem 128. FIG. 1 provides an example. Pressure regulating system 128includes a pressure gauge 123 and a controller 125. In some embodiments,pressure regulating system 128 regulates pressure by adding or removingfluid 129 from the space between rigid shell 121 and liner 131 using apump 127.

Buffer tank 145 connects to storage containers 105 through a conduit119. In some embodiments, the conduit 147 that connects buffer tank 145to dispensing system 160 and conduit 119 exit container space 140 at aheight below head space 143. This design can improve venting of headspace 140. In some embodiments, conduit 147 taps container space 140proximate its upper end as shown in the examples of FIGS. 1, 2, and 4.This design can provide a more consistent pressure head for pump 163. Insome other embodiments, conduit 147 taps container space 140 proximateits lower end as shown in the examples of FIGS. 3 and 5. This design canreduce the probability that bubble will be entrained in chemicalsolution 150 when it is supplied to dispensing system 160. Depending onother design choices, one or the other configuration for conduit 147 canfacilitate expansion and contraction of container space 140 byminimizing tubing within container space 140. Similar considerationsapply, and there are corresponding embodiments, for connecting conduit119 to buffer tank 145. In some embodiments, the lengths of any tubeswithin container space 140, such as tubes connecting with conduits 119or 147, are all less than half the height of container space 140.

Storage containers 105 are detachable from supply system 101. They arereplaced when more of chemical solution 150 is required in buffer tank145. Storage containers 105 can be attached to the conduit 119 thatconnects storage containers 105 to buffer tank 145 through a coupling111. In some embodiments, conduit 119 includes a valve 103 that preventsbackflow from buffer tank 145 when a storage container 105 is detachedfrom coupling 111. In some embodiments, valve 103 is a check valve. Insome embodiments, valve 103 includes a mechanism for releasing gastrapped in conduit 119.

Whereas storage containers 105 are detachable from photolithographychemical supply system 101, buffer tank 145 can remain permanentlyconnected to dispensing system 160. Accordingly, in some embodimentsconduit 147 provides a fixed connection between buffer tank 145 anddispensing system 160.

Buffer tank 145 is designed with sufficient capacity to receive and holdthe contents of a storage container 105 filled to capacity. In mostembodiments, storage containers 105 have a capacity that is greater than3 liters. Accordingly, in most embodiments, buffer tank 145 has astorage capacity greater than 3 liters. Storage capacity refers tooverall capacity as opposed to free capacity at a given time, whichdepends on the amount of chemical solution 150 currently in containerspace 140. The storage capacity of container space 140 corresponds toits maximum volume.

In some embodiments, storage containers 105 are designed to drain fromthe bottom. More specifically, in some embodiment storage containers 105have an opening 109 at and through their bottoms through which chemicalsolution 150 can be drained. In some embodiments, storage containers 105have a bottom surface 107 sloping inward toward a bottom-drainingopening 109. Bottom draining can reduce the chance for entrainingbubbles. Bottom draining can reduce agitation at an interface 104between chemical solution 150 and gas in head space 106, reducing ratesof absorption from gas in head space 106.

In most embodiments, storage containers 105 are configured to be drainedwithout exposing chemical solution 150 to air. In some embodiments,storage containers 105 are rigid containers. In some embodiments,storage containers 105 are connected by a line no to a nitrogen storagecylinder 190, which allows head space 106 to fill with nitrogen aschemical solution 150 drains. In some embodiments, storage containers105 are elevated relative to buffer tank 145 allowing drainage to begravity driven. In some embodiments, nitrogen storage cylinder 190 isconfigured to apply a positive pressure in head space 106 sufficient todrive chemical solution 150 out of storage container 105 and into buffertank 145. In some embodiments, storage container 105 is avariable-volume container. In some of these embodiments, storagecontainer 105 has one of the variable volume designs as described forbuffer tank 145. Storage container 105 has corresponding embodimentsincluding embodiments corresponding to the various ways in whichpressure can be applied.

In most embodiments, chemical solution 150 is stored for days, weeks, ormonths in storage containers 105. In some embodiments, storagecontainers 105 are containers in which chemical solution 150 is shipped.A manufacturer may be requested to supply chemical solution 150 instorage containers 105 designed for use in photolithography system 100,whereby there is no risk of contaminating chemical solution 150 prior toattaching storage containers 105 to supply system 101.

FIG. 6 provides a flow chart of a method 200 according to someembodiments of the present disclosure. Method 200 is a method forsupplying a chemical solution 150 to a photolithography system 100.Method 200 includes act 201, which is pumping chemical solution 150 frombuffer tank 145 and applying it to wafers 180. In some embodiments,chemical solution 150 is drawn from buffer tank 145 each time dispensingsystem 160 makes an application of chemical solution 150 to a wafer 180.The volume of the container space 140 decreases as chemical solution 150is removed.

Act 203 is determining whether buffer tank 145 is in need of refill. Insome embodiments, the amount of chemical solution in buffer tank 145 isdetermined by a sensor, such as a sensor detecting the height of apiston 132. In some embodiments, the amount of chemical solution inbuffer tank 145 is determined by a controller 125 monitoring the amountof fluid 129 in a space between liner 131 and shell 121. In someembodiments, a low state of buffer tank 145 is inferred by a controllerthat monitors the amount of chemical solution 150 that has beendispensed by dispensing system 160 since the last refill of buffer tank145. If a refill is needed, method 200 proceeds with a series of acts210 constituting a refill operation.

In some embodiments, dispensing system 160 continues to operate duringrefill operation 210. In these embodiments, buffer tank 145 allowsphotolithography chemical supply system 101 to continuously supplydispensing system 160, which improves productivity.

Refill operation 210 begins with act 211, attaching a storage container105 filled to capacity with chemical solution 150 to supply system 101.In some embodiments, this includes attaching conduit 119 to an opening109 at the bottom of storage container 105 through a coupling 111. Insome embodiments, act 211 includes attaching a nitrogen supply line 110to the top of storage container 105.

Act 213 is opening a valve 103 that controls communication betweenstorage container 105 and buffer tank 145. In some embodiments, act 213is preceded by pressurizing the contents of storage container 105 to ahydrostatic pressure at or slightly above that in buffer tank 145. Insome embodiments, act 213 is preceded by expelling gas trapped inconduit 119. A valve 103 can be designed for that function.

Act 215 is draining the contents of storage container 105 into buffertank 145. In some embodiments, act 215 is a continuous operation throughwhich storage container 105 drains steadily until empty. In someembodiments, act 215 is carried out from start to finish over arelatively short period. A short period is less than 5 minutes. Bycomparison, in most embodiments refill operation 210 is carried out lessthan once per hour. Once per day, for example.

Draining storage container 105 from a full condition to an emptycondition over a short period minimizes the risk of contaminationoccurring or gases being absorbed into chemical solution 150 whilestorage container 105 is in a partially full state. In most embodiments,the volume of container space 140 increases by an amount thatapproximately equals the capacity of storage container 105 over thecourse of act 215.

Act 217 is closing valve 103, allowing the empty storage container 105to be removed supply system 101 and allowing supply system 101 to beoperated independently from storage container 105. Closing valve 103prevents backflow from buffer tank 145. In some embodiments, valve 103is a check valve and closes by itself. Accordingly, act 217 is optional.

Refill operation 210 continues with another optional act, adjusting thepressure in buffer tank 145. In some embodiments, the pressure in buffertank 145 is regulated. In some of these embodiments, pressure regulationis suspended during refill operation 210. Act 219 may then be employedto adjust the pressure in buffer tank 145 to a desired pressure forsupplying dispensing system 160.

Act 221 is another optional act. In some embodiments, dispensing system160 is prevented from drawing from buffer tank 145 during refilloperation 210. In some of these embodiments, act 221 is employed. Act221 is continuing to suspend dispensing from buffer tank 145 though awaiting period during which the contents of container space 140 areallowed to settle and any bubbles that form or have been entrained areallowed time to rise into head space 143. In some embodiments, a waitingperiod is in the range from one minute to half an hour. In someembodiments, a waiting period is in the range from five minutes tofifteen minutes.

Method 200 continues with an option act 205, determining whether thepressure in buffer tank 145 is too low. If it is too low, method 200proceeds with act 223, which is increasing the pressure in buffer tank145. In some embodiments, acts 205 and 223 are replaced by a processcontrol loop. In some embodiments, a process control loop can eitherincrease or decrease the pressure in buffer tank 145. A desired pressurefor buffer tank 145 is a positive pressure. In some embodiments, thepressure in buffer tank 145 is maintained in the range from 1.01 to 1.3atm.

Method 200 continues with act 207, determining whether there are bubblesin head space 143. Act 207 is also optional. If there are bubbles inhead space 143, method 200 continues with act 225, opening venting valve141. After a brief fixed period, venting valve 141 is closed by act 209.In some other embodiments, venting valve 141 is held open until bubblesare no longer detected in head space 143.

Method 200 limits chemical solution 150's contact with and absorption ofgases. In some embodiments, chemical solution 150 is provided inchemical solution storage containers 105 with oxygen and nitrogenconcentrations substantially below their concentrations at equilibriumwith ambient air. In some embodiments, supply system 101 provideschemical solution 150 to chemical solution dispensing system 160 withoxygen and nitrogen concentrations substantially and consistently belowtheir concentrations at equilibrium with ambient air. A concentration10% below equilibrium would be considered substantially below.

The present disclosure provides a photolithography system including avariable-volume buffer tank, a dispensing system connected to the buffertank and configured to dispense a photolithography chemical solutionfrom the buffer tank onto wafers, and a valve configured to release gasfrom a head space of the buffer tank while blocking the release ofliquid from the head space. The buffer tank can be operated to providethe chemical solution to the dispensing system while keeping thechemical solution from contact with air and other gases.

The present disclosure also provides a photolithography chemical supplysystem that includes a storage container having an opening at the bottomand a variable-volume buffer tank coupled to the storage containerthrough the opening at the bottom. The buffer tank has a greater storagecapacity than the storage container. This system can be used to providephotolithography chemicals to the buffer tank while limiting contactbetween the photolithography chemicals and air or other gas whiledraining or otherwise remaining within the partially full storagecontainer.

The present disclosure provides a method of supplying a chemicalsolution to a photolithography system. The method includes pumping thechemical solution from a variable-volume buffer tank, dispensing thepumped chemical solution in a spin-coater, and refilling the buffer tankby emptying a storage container filled with the chemical solution intothe buffer tank.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A photolithography system, comprising: avariable-volume buffer tank; a dispensing system connected to thevariable-volume buffer tank and configured to dispense aphotolithography chemical solution from the variable-volume buffer tankonto wafers; and a valve configured to release gas from a head space ofthe variable-volume buffer tank while blocking the release of liquidfrom the head space; wherein the variable-volume buffer tank includes aphotolithography chemical solution inlet and a photolithography chemicalsolution outlet through which the photolithography chemical solutionconcurrently flow when being provided to the dispensing system.
 2. Thephotolithography system of claim 1, further comprising: a storagecontainer having a storage capacity volume; and a connector forming aconnection for transferring fluid from the storage container to thephotolithography chemical solution inlet of the variable-volume buffertank; wherein the variable-volume buffer tank has a maximum volume thatis greater than the storage capacity volume of the storage container. 3.The photolithography system of claim 2, wherein the connection fortransferring fluid from the storage container to the buffer tank isconfigured to drain the contents of the storage container from out ofthe bottom of the storage container.
 4. The photolithography system ofclaim 1, wherein the buffer tank comprises a collapsible liner within arigid shell.
 5. The photolithography system of claim 1, wherein thebuffer tank comprises a piston and cylinder arrangement.
 6. Thephotolithography system of claim 1, wherein the buffer tank comprises aflexible container with accordion pleats.
 7. The photolithography systemof claim 1, wherein the valve is an electronically controlled valve. 8.The photolithography system of claim 7, further comprising: a bubbledetector configured to detect bubbles in the head space; wherein thevalve is configured to open automatically in response to detection ofbubbles in the head space by the bubble detector.
 9. Thephotolithography system of claim 1, wherein the variable-volume buffertank connects to the photolithography chemical solution dispensingsystem through an opening that exits the buffer tank at a height belowthe head space.
 10. The photolithography system of claim 1, wherein thedispensing system comprises a positive displacement pump operative todiminish the volume of the buffer tank with each displacement cycle. 11.The photolithography system of claim 1, wherein the buffer tankcomprises a pressure-regulating system.
 12. The photolithography systemof claim 1, wherein the photoresist chemical solution inlet opening andphotoresist chemical solution outlet opening are each arranged in asidewall of the variable-volume buffer tank, and wherein the valve isarranged above both the photoresist chemical solution inlet opening andthe photoresist chemical solution output opening and configured torelease the gas through a gas-vent opening arranged in an upper regionof the variable-volume buffer tank.
 13. A photolithography system,comprising: a variable-volume buffer tank; a dispensing system coupledto the variable-volume buffer tank and configured to dispense aphotolithography chemical solution from the variable-volume buffer tankonto wafers; a valve configured to release gas from a head space of thevariable-volume buffer tank while blocking the release of liquid fromthe head space; and a bubble detector configured to detect bubbles inthe head space, and configured to selectively trigger opening of thevalve based on whether bubbles are detected in the head space; whereinthe variable-volume buffer tank includes a photolithography chemicalsolution inlet and a photolithography chemical solution outlet throughwhich the photolithography chemical solution concurrently flow whenbeing provided to the dispensing system.
 14. The photolithography systemof claim 13, wherein the variable-volume buffer tank comprises acollapsible liner within a rigid shell.
 15. The photolithography systemof claim 13, wherein the variable-volume buffer tank comprises a pistonand cylinder arrangement.
 16. The photolithography system of claim 13,wherein the variable-volume buffer tank comprises a flexible containerwith accordion pleats.
 17. The photolithography system of claim 13,further comprising: a storage container having a storage capacityvolume; and a connector forming a coupling for transferring fluid fromthe storage container to the variable-volume buffer tank; wherein thevariable-volume buffer tank has a maximum volume that is greater thanthe storage capacity volume of the storage container.
 18. Thephotolithography system of claim 17, wherein the coupling fortransferring fluid from the storage container to the variable-volumebuffer tank is configured to drain the contents of the storage containerfrom out of the bottom of the storage container.
 19. Thephotolithography system of claim 13, wherein the variable-volume buffertank couples to the photolithography chemical solution dispensing systemthrough an opening that exits the variable-volume buffer tank at aheight below the head space.
 20. A photolithography system, comprising:a storage container having a storage capacity volume and configured tostore a photolithography chemical solution; a variable-volume buffertank having a photolithography chemical solution inlet and aphotolithography chemical solution outlet, wherein the aphotolithography chemical solution inlet is configured to receive thephotolithography chemical solution from the storage container through aconnector, wherein the variable-volume buffer tank has a maximum volumethat is greater than the storage capacity volume of the storagecontainer; a dispensing system coupled to the photolithography chemicalsolution outlet and configured to dispense a photolithography chemicalsolution from the variable-volume buffer tank onto wafers, wherein thephotolithography chemical solution concurrently flows through thephotolithography chemical inlet and the photolithography chemicalsolution outlet when being provided to the dispensing system; and avalve configured to release gas from a head space of the variable-volumebuffer tank while blocking the release of liquid from the head space.